Eastern Alps - University of Innsbruck

Mitt. Österr.Geol. Ges.
ISSN0251-7493
86(1993)
j
S. 6 1 - 7 4
Wien, August 1994
miii'fiHi
Austria
Eastern Alps
Graywacke Zone
Paleogeography
Thrusting
Revised Lithostratigraphy and Structure
of the Eastern Graywacke Zone
(Eastern Alps)
mckskmned tectonics
FRANZ NEUBAUER, ROBERT HANDLER, SIEGFRIED H E R M A N N & G E R N O T PAULUS*)
7 Text-Figures, 1 Table
Contents
1.
2.
3.
4.
5.
6.
Zusammenfassung
Abstract
Introduction
Litho- and Tectonostratigraphyofthe Eastern Graywacke Zone
2.1. Veitsch Nappe
2.2. Silbersberg Nappe
2.3. Kaintaleck Nappe
2.4. Noric Nappe
Alpidic vs. Pre-Alpidic Metamorphism
Alpidic Ductile Deformation
Discussion
Conclusions
Acknowledgements
References
61
61
62
62
62
64
65
68
70
70
71
72
72
72
Revision der Lithostratigraphie und Struktur
der östlichen Grauwackenzone
(Ostalpen)
Zusammenfassung
Der oberostalpine Deckenstapel der östlichen Grauwackenzone wurde neu kartiert und petrographisch, strukturell und geochronologisch untersucht. Entgegen älteren Auffassungen besteht die östliche Grauwackenzone aus vier alpidischen Decken, die sich in Grundgebirgslithologie, jungpaläozoisch/triadischen Hüllsedimenten und präalpidischer metamorpher Überprägung unterscheiden. Wir unterscheiden vom Liegenden zum Hangenden zwischen der Veitscher Decke, der Silbersbergdecke, der Kaintaleckdecke und der Norischen
Decke, zu der tektonisch auch die basalen Anteile der Nördlichen Kalkalpen gehören.
Die Veitscher Decke besteht aus karbonischen molasseähnlichen Klastika und Karbonaten und möglichen permischen Rotsedimenten.
Die neu eingeführte Silbersbergdecke setzt sich aus einem quarzphyllitischen Grundgebirge (Altpaläozoikum?), einem verrucanoähnlichen
Deckgebirge (Perm?) und dem alkalinen Gloggnitzer Riebeckitgneis zusammen. Die ebenfalls neu eingeführte Kaintaleckdecke besteht aus
altpaläozoisch amphibolitfaziell metamorphen Grundgebirgsserien und Schuppen, die sowohl vom Hangenden wie Liegenden der Decke
eingeschuppt sind. Diese Grundgebirgseinheiten stammen möglicherweise von mehreren unabhängigen tektonischen Einheiten. Wichtig
sind Amphibolite mit geochemischer Affinität zu mittelozeanischen Rückenbasalten und Intrapiattenbasalten, Serpentinite, migmatitische
Paragneise, Glimmerschiefer, Quarzite und Marmore, sowie Pegmatit- und Aplitgneise. Die Norische Decke beinhaltet ordovizische bis
unterkarbonische siliziklastische Sedimente, saure ordovizische Vulkanite, silurische Metabasite und vorwiegend devonische Karbonate.
Die Stapelung dieser Einheiten erfolgte in der Unter- bis Oberkreide unter niedriggradig metamorphen Bedingungen mit duktiler, meist
west- bis nordwestgerichteter einfacher Scherung. Eine qualitative Bilanzierung des ostalpinen Deckenstapels deutet an, daß die Silbersbergdecke als Liegendeinheit der Nördlichen Kalkalpen betrachtet werden kann, die durch Bifurkation und vorlandgerichtetes Klettern des
basalen, ostalpinen Abscherhorizontes von der Norischen Decke einschließlich der Nördlichen Kalkalpen getrennt wurde.
Abstract
The Upper Austroalpine Nappe Complex of the eastern Graywacke Zone has been examined by field mapping, petrographical, structural,
and geochronological studies. In contrast to previous studies evidence was found of four major Alpine thrust sheets which can be subdivided by their basement lithologies, their Late Paleozoic to Triassic cover sequences, and the extent of pre-Alpine metamorphism. We
distinguish between the following thrust sheets (from footwall to hangingwall): The Veitsch nappe, the Silbersberg nappe, the Kaintaleck
nappe, and the Noric nappe.
*) Authors' addresses: FRANZ NEUBAUER, Institut für Geologie und Paläontologie, Paris-Lodron-Universität, Hellbrunnerstraße 34, A-5020
Salzburg; ROBERT HANDLER, SIEGFRIED HERMANN & GERNOT PAULUS, Institut für Geologie und Paläontologie, Karl-Franzens-Universität,
Heinrichstraße 26, A-8010 Graz.
62
F. NEUBAUER, R. HANDLER, S.:HERMANN&G. PAULUS
The Veitsch nappe includes clastic and carbonatic post-Variscan molasse-like sequences of Carboniferous and possibly even Permian
age. The Silbersberg nappe (new term) is composed of a quartzphyllite basement of supposed early Paleozoic age, an "Alpine-Verrucano"-type cover of probable Permian age, and mylonitic alkaline metavolcanics (Gloggnitz Riebeckite Gneiss). The Kaintaleck nappe (new
term) generally includes amphibolite facies metamorphic rocks of various Iithologies imbricated with low grade metamorphic rocks from
both footwall and hangingwall units. The basement Iithologies are probably derived from several independent basement complexes, including various amphibolites with both MOR- and WP-basalt-like geochemical signatures, serpentinites, migmatitic paragneisses, micaschists,
quartzites, and thin marbles. Some of these basement complexes are intruded by pegmatites and aplitic gneisses. The Noric nappe
contains Ordovician to Carboniferous siliciclastic sediments, Ordovician acidic voicanics, Silurian metabasites, and Devonian carbonate
sequences. The Noric nappe is unconformably covered by Permo-Mesozoic sequences of the Northern Calcareous Alps.
The assembling of all these units occurred during the Early to Middle Cretaceous thrusting under low grade metamorphic conditions,
forming ductile, top to the W- to NW-directed fabrics. The qualitative balancing of the Austroaipine nappe pile suggests that the Silbersberg
nappe may be the footwall extension of a part of the Northern Calcareous Alps. The Silbersberg nappe is believed to be separated from the
Noric nappe by bifurcation and foreland-directed climbing of the decollement surface during Cretaceous thrusting.
1. Introduction
The eastern Graywacke Zone plays an important role in
the evaluation of the intra-Austroalpine nappe structure
within the Eastern Alps (Text-Fig. 1). The basic observation
is the well-known superposition of a thrust sheet, containing
an early Paleozoic basement and the Permian to Mesozoic
cover sequences of the Northern Calcareous Alps, overfossil-bearing Carboniferous sediments of the Veitsch nappe
along the Noric Thrust ('Noric Line') within the Graywacke
Zone. This structure and its suggested extension to central
and southern portions of the Austroaipine Nappe Complex,
often combined with the Upper Austroaipine Nappe Complex, proves that a large amount of displacement in the scale
of at least 150 kilometers occurred (TOLLMANN, 1959, 1987;
FLÜGEL, 1960). Other arguments in favor of a limited displacement along the basal Upper Austroaipine thrust surface have also been proposed (FRANK, 1987). Recently the
significance of the thrust is stressed because of the observation of Triassic deep sea sediments along the southern
margin of the Northern Calcareous Alps (KOZUR and MOSTLER, 1992). Furthermore, investigations in the last few years
suggest that the structure along the Noric Line is more complicate than previously supposed (NIEVOLL, 1984; HERMANN
etal., 1992b).
Especially in the Kaintaleck complex, mainly amphibolite
facies metamorphic rocks which are situated along the
nappe contact, have been suggested to represent the preLate Ordovician basement of the Noric nappe (DAURER &
SCHÖNLAUB, 1978; NEUBAUER, 1985). On the other hand,
NIEVOLL (1984) suggested that clastic sequences below the
Kaintaleck basement may represent Verrucano-type Permian elastics.
In this study we present new field observations and petrographical data concerned with the lithostratigraphy from
several areas along strike of the Noric thrust (e.g., HERMANN,
1992; PAULUS, 1992; HANDLER, 1994) that argue for a more
complicate stratigraphy and structure of the eastern Graywacke Zone. We discuss these data together with new results from geochronological and structural studies, which
will be presented elsewhere (HANDLER et al., submitted; NEUBAUER et al., in prep.). The main goal in this paper is to show
the significance of our new field data in conjunction with the
intra-Austroalpine nappe structure.
2. Litho- and Tectonostratigraphy
of the Eastern Graywacke Zone
In this study new data from the following areas are discussed: the area east of Brück a.d. Mur (Text-Fig. 2);
Kaintaleck and Oberdorf a.d. Laming (Text-Fig. 3) and
Gloggnitz-Vöstenhof (Text-Fig. 4). The basic data of all tectonostratigraphic units have been compiled in Table 1. Also
included are representative cross sections from all areas
mentioned above (Text-Fig. 5) and a tectonostratigraphic
scheme (Text-Fig. 6).
The Middle Austroaipine basement complexes (Rennfeld-Mugel and Troiseck-Floning crystalline complexes) and
the Permian to Triassic cover sequences occur below the
structural base of the Graywacke Zone (Text-Figs. 1, 6). The
Middle Austroaipine cover consists of Verrucano-type clastic to volcanic sequences (Rannach Fm.) of supposed Permian age, rauhwackes and fossil-bearing Middle Triassic dolomites and limestones ("Triassic of Thörl"; TOLLMANN, 1963,
1968; NEUBAUER, 1988a). The geological time scale of HARLAND et al. (1989) is used for calibrations between biostratigraphy and chronostratigraphy.
2 . 1 . Veitsch Nappe
The Veitsch nappe contains a continuous stratigraphic
section that includes fossil-bearing Early and Late Carboniferous formations (RATSCHBACHER, 1987; RATSCHBACHER &
NIEVOLL, 1984; KRAINER, 1992; NIEVOLL, 1983) extending in-
to possibly Permian clastic sequences (NEUBAUER & VoZAROVÄ, 1990). We propose renaming the sequence of all
these formations as the Veitsch Group.
RATSCHBACHER (1987) introduced a subdivision of the Carboniferous part of the Veitsch Group into three formations:
from footwall to the hangingwall he distinguished the Steilbachgraben Fm., composed mainly of elastics and minor
carbonates, the Triebenstein Fm. with carbonates and some
greenschists and the Sunk Fm. with preferably quartz conglomerates, and anthracite/graphite deposits. In the eastern portions, the Veitsch Group exhibits a similar threefold
subdivision with elastics which are separated by a carbonate horizon.
The hangingwall greyish elastics of the Sunk Fm. grade
into the Graschnitz Fm. (NEUBAUER & VOZAROVÄ, 1990) that
includes light-coloured, brownish to reddish sandstones,
phyllites, and rare quartz breccias. The only major exposures occur north of the village of Frauenberg east of
Brück a.d. Mur (Text-Fig. 2; FLÜGEL et al., 1990). This section is estimated to represent approximately several tens of
metres in structural thickness. The sandstones and breccias form dm-scaled intercalations within the predominant
phyllites/metasiltstones. Along the basal portions of the
section, 0,1 metres thick acidic tuffaceous intercalations including quartz and alkali feldspar megacrysts occur.
Text-Fig. 1.
Tectonic map of eastern portions of the northeastern Alps including the eastern Graywacke Zone.
»
Revised Lithostratigraphy and Structure of the E.
3rn Graywacke Zone (Eastern Alps)
63
64
2.2. Silbersberg Nappe
We introduce the Silbersberg nappe to summarize a number of formations that are clearly tectonically separated from
all other footwall and hangingwall formations. These include
F. NEUBAUER, R. HANDLER, S. HERMANN & G. PAULUS
all formations below the metamorphic Kaintaleck Complex
already known from previous maps by CORNELIUS (1952),
LESKO (1960) and NIEVOLL (1984).
These formations include quartzphyllite and carbonatechlorite schists which occur at the tectonic base of the
Text-Fig. 2.
Simplified geological map of the Graywacke Zone east of Brück a.d. Mur.
For location, see Text-Fig. 1; for legend, see opposite page.
Revised Lithostratigraphy and Structure of the Eastern Graywacke Zone (Eastern Alps)
nappe, the Gloggnitz Riebeckite Gneiss and the Silbersberg Conglomerate (Text-Fig. 6).
The carbonate chlorite schists include greenish, well-foliated
chlorite-carbonate schists and intercalated chlorite schists.
These schists occur with a structural thickness of c. 100 metres
65
above the Veitsch nappe in the Oberdorf area (TextFig. 3). The quartzphyllite occurs both SW of the Kaintaleck and the Gloggnitz area (Text-Fig. 3, 4). The
thickness of the quartzphyllite including all intercalations is appr. 100 metres in the Gloggnitz area. Here,
thick lenses of foliated felsic volcanics occur. These
are mainly composed of feldspar and minor quartz
suggesting a more intermediate composition. Other
intercalations observed are greenschists with alkaline
geochemical composition (PAULUS, 1992; PAULUS &
Alluvial deposits
NORIC NAPPE
Phyllite
NEUBAUER, in prep.). The Gloggnitz Riebeckite Gneiss
occurs along the boundary between the quartzphyllite
and the Silbersberg Conglomerate. The gneiss is a
fine-grained mylonite which contains quartz/feldspar,
riebeckite and rare clinopyroxene.
The geochemical signature of the gneiss suggests a
highly fractionated volcanic protolith (KOLLER & ZEMANN, 1991; PAULUS, 1992; PAULUS & NEUBAUER, in
V- -V -V
Greenschist
KAINTALECK NAPPE
prep.). A Rb-Sr whole rock errorchrone of ca. 132±12
Ma is interpreted to represent either a middle Cretaceous age of protolith formation or dating the age of
the Cretaceous metamorphic overprint (PAULUS,
1992; PAULUS & NEUBAUER, in prep.). The quartzphyl-
Kalwang(?) Conglomerate
I v v «y v v
<2£22s
Amphibolite
>
Garnet amphibolite
Mica Schist/Paragneiss
SILBERSBERG NAPPE
Alpine Verrucano
VEITSCH NAPPE
Graschnitz Fm.
Grey and black Phyllite
(Sunk and Triebenstein Fm.)
Sandstone (Sunk Fm.)
0 o a o o o o
O 0 0 0 0 0 0
o o o o o o ~
Quartz Conglomerate (Sunk Fm.)
Triebenstein Fm.
lite and carbonate chlorite schists closely resemble
early Paleozoic quartzphyllite which are widespread
throughout the Austroalpine units (e.g., SCHÖNLAUB,
1979; NEUBAUER SSASSI, 1993).
The main constituents of the Silbersberg Nappe are
light-coloured greenish quartzitic phyllites, which include thin layers of acidic tuffs and quartz breccias.
Here all constituents are interpreted to represent the
Alpine Verrucano Fm., and the Silbersberg Conglomerate. In both formations, quartz clasts dominate
and often exhibit a reddish colour. Other constituents
are minor carbonate clasts, detrital white mica and
some local micaschist and orthogneiss clasts were
observed.
In accordance with previous suggestions (NIEVOLL,
1984) we interpret that both, the Silbersberg Conglomerate and Alpine Verrucano Fm.' represent deposits of Permian age supported by the following arguments:
1) the general habit is similar to the 'Alpine Verrucano
Fm.' in other Austroalpine units such as the Semmering-Wechsel units (e.g., TOLLMANN, 1977);
2) the general dissimilarity with early Paleozoic formations in the region;
3) the intercalations of acidic tuffs which are similar to
other intercalations of this kind in the 'Alpine Verrucano Fm.' elsewhere; and
4) the inclusions of reddish quartz pebbles which are
preserved although Cretaceous metamorphism.
Until now such reddish pebbles were found in the
Alps only in Permian deposits.
MIDDLE AUSTROALPINE NAPPE
2.3. Kaintaleck Nappe
Rannach Quartzite (Permo-Scythian?)
The "Kaintaleck slices" occur within the eastern
Graywacke zone along 70 km of a thrust surface
Alpine Verrucano (Permian?)
(HAUSER, 1938; CORNELIUS, 1941,1952). The structur-
Rennfeld-Mugel Basement Complex
al thickness of the Kaintaleck slices does not exceed
two hundred metres. In some areas these slices are
intensely imbricated with footwall and hangingwall
rocks as in the Brück and Kaintaleck areas (TextFig. 3) (NEUBAUER et al., 1987; RATSCHBACHER & NEU-
BAUER, 1989; HERMANN, 1992). Lithologies, geochro-
66
F. NEUBAUER, R. HANDLER, S. HERMANN&G. PAULUS
Revised Lithostratigraphy and Structure of the
Alluvial Deposits
NORIC NAPPE
Alpine Verrucano
Paleozoic Limestone
Chert
Rad Phyllite
f 4-
H
Blasseneck Porphyroid
Phyllite
Greenschist
KAINTALECK NAPPE
Kalwang(?) Conglomerate
Amphibolite
Micaschist / Paragneiss
SILBERSBERG NAPPE
Alpine Verrucano
Gloggnitz Riebeckite Gneiss
H
Quartz- and Calcareous Phyllite
Porphyroid
Greenschist
VEITSCH NAPPE
Alpine Verrucano
Grey and Black Phyllite
Limestone
MIDDLE AUSTROALPINE NAPPE
Alpine Verrucano
Rennfeld-Mugel Basement Complex
Thrust Surface
Fault
;Zone (Eastern Alps)
37
nological data, geological relationships, and the structural
position suggest that the Kaintaleck slices consist of various
lithotectonic units. This subdivision is mainly based on work
in the area near Brück a.d. Mur (NEUBAUER & FRISCH, 1993).
1) The R i t t i n g c o m p l e x occurs near Bruck/Mur, at the
Kaintaleck, and west of Vöstenhof. It is composed of garnet-zoisite amphibolite, serpentinite, micaschist and thin
marble layers. The chemistry of the amphibolites corresponds to tholeiite basalts (NEUBAUER et al., 1989b;
PAULUS, 1992). At the Kaintaleck geochemical analyses
point consistently to transitional within plate-basalt affinities (HERMANN, 1992; HERMANN et al., 1992a). In the
Brück area amphibolites contain a disseminated Cu
mineralization. Chromite occurs in the serpentinites
(NEUBAUER et al., 1989). The protolith age of the Ritting
complex is uncertain.
2) The F r a u e n b e r g c o m plexis exposed inan area near
Bruck/Mur (Text-Fig. 2) and near Oberdorf (Text-Fig. 3).
It is mainly composed of paragneiss containing plagioclase amphibolite and marble lenses. The petrographic
characteristics are at a contrast with those of the Ritting
complex. The amphibolites exhibit a mildly alkaline trend.
A hornblende-garnet gneiss from the Bruck/Mur region
which is included in the plagioclase amphibolite contains
numerous rounded zircons with smooth surfaces, which
are interpreted as the result of high-grade metamorphism. Pressure and temperature conditions are uncertain,
but a high-pressure event is indicated by the high pyrope
content in garnet (ca. 40 mole percent pyrope). The zircons yielded an U-Pb upper intercept age of ca. 2.53 Ga
and a lower intercept age of 516 Ma (NEUBAUER et al.,
1989b). Due to this highly discordant pattern, the upper
intercept age is considered to be the protolith age, assuming an igneous source of the hornblende-garnet
gneiss, and the lower intercept refers to the late Cadomian age of metamorphism (NEUBAUER et al., 1989b).
Brown colored, metamict zircons yield an upper intercept age of approximately 2.8 Ga. These zircons are
interpreted to represent crustal contamination of the igneous source rock (NEUBAUER et al., in prep.).
3) The P r i e s e l b a u e r c o m p l e x is exposed near
Bruck/Mur, Oberdorf, and west of Vöstenhof. It is composed of migmatitic augen paragneiss and micaschists
including minor occurrences of amphibolite as well as
concordant and discordant aplites. Zircons from the paragneiss yielded a lower intercept U-Pb zircon age of ca.
391 Ma which is interpreted as being the approximate
age of metamorphism. A discordant aplitic vein yielded
an upper intercept zircon age of 363 Ma which reflects
the zircon crystallization within the protolith (NEUBAUER et
al., 1987; in prep.). The Prieselbauer complex has been
interpreted as the basement of the Carboniferous sediments of the Veitsch nappe (NEUBAUER & FRISCH, 1993).
The Ritting and Frauenberg complexes are transgressively covered by equivalents of the Kalwang (Gneiss) Conglomerate that has been interpreted to represent the stratigraphic base of the fossiliferous Late Ordovician sequences
of the Noric Group (DAURER & SCHÖNLAUB, 1978; NEUBAUER,
1985; LOESCHKEet al., 1990). Apart from various basement
fragments, such as amphibolites and serpentinites, trondhjemitic orthogneiss components dominate the conglomerate. The orthogneiss is interpreted to be derived from
a plutonic source in a supra-subduction zone environment
because of its geochemical patterns, especially those of
the REEs. The U-Pb zircon upper intercept ages of two
boulders from different localities are approximately 500 Ma
68
F. NEUBAUER, R. HANDLER, S. HERMANN &G. PAULUS
Text-Fig. 4.
Simplified geological map of
the Gloggnitzarea.
For location, see Text-Fig. 1; for
legend, see Text-Fig. 3.
(NEUBAUER et al., 1987). The
dominance of the orthogneiss clasts suggests the
presence of a major pluton
in the hinterland of the
conglomerates. This orthogneiss is not known to occur in the Kaintaleck slices.
Previously it was argued
that the Kalwang (Gneiss)
Conglomerate might be the
stratigraphic base of the
Noric Group (DAURER &
SCHÖNLAUB,
1978;
NEU-
BAUER, 1985). The conglomerate at the locality Frauenberg (Text-Fig. 2) follows
the Kaintaleck Complex
along a sedimentary contact (NEUBAUER, 1985). Age
data for metamorphism and
magmatism ranging from
520 to 360 Ma preclude that
interpretation. Furthermore,
detailed
mapping
by
LOESCHKE
et
al.
GL0GGNITZ
(1990)
showed thrust surfaces
separating the Kalwang
Conglomerate from the
equivalents of -the Ordovician Gerichtsgraben Formation.
Recent
mineral
ages
(Rb/Sr and 40Ar/39Ar muscovite and amphibole) of all
three complexes of the
Kaintaleck nappe resulted
in ages ranging between 420 and 360 Ma with no significant
difference between these three complexes (DALLMEYER et
al., 1992; HANDLER et al., 1993, submitted). Therefore, a major Mid-Paleozoic tectonothermal event affected major portions of the "Kaintaleck slices".
In nearly all areas the ductile shear zones separate the
Kaintaleck lithologies from other adjacent units. Similar ductile shear zones in the scale of one to ten metres also occur
within the Kaintaleck complex sometimes forming "pseudoconglomerates" with boudins of competent lithologies
within a ductilely deformed mica-rich matrix.
>FURTH
LAUB et al., 1980; SCHÖNLAUB, 1982; NIEVOLL, 1987) and a
fossil-free portion below the fossil-bearing Late Ordovician
rocks. Internal stratigraphy of the Noric Group has yet to be
completely resolved in the study area.
Besides the Late Ordovician to Devonian carbonate-dominated sections in the central portions, the eastern Graywacke zone contains wide regions of siltstone and phyllite,
and minor mafic volcanic rocks. The phyllite is related to
sections occurring with thin Devonian pelagic limestones
(NIEVOLL, 1987; SCHÖNLAUB, 1982).
The structural base of the Noric Group is dominated by up
to ca. 1000 metre thick, partly arkosic phyllite (Gerichtsgraben Fm.) which contains thin greenstone layers, acidic
2.4. Noric N a p p e
tuffs, and metasandstones (DAURER & SCHÖNLAUB, 1978;
The Noric Nappe consists of a thick continuous sequence
of clastic, volcanic, and carbonate-dominated formations
for which we have introduced here the term Noric Group. In
the study area, the Noric Group includes sequences from
Late Ordovician to the Visean-Namurian boundary (SCHÖN-
HERMANN, 1992). Especially in the Kaintaleck area, the up to
30 metres thick Kaintalgraben Porphyroid (Text-Fig. 3;
HÄUSER, 1938; HERMANN, 1992) forms a continuous volcanogenic layer several hundreds metres below the Blasseneck Porphyroid. This horizon may be correlated with
LOESCHKE, 1989; LOESCHKE et al., 1990; SCHÖNLAUB, 1982;
69
Revised Lithostratigraphyand Structure of the Eastern Graywackc Zone (Eastern Alps)
NNW
SSE
NNE
SSW
P I
Text-Fig. 5.
Sections of the eastern Graywacke Zone.
For locations, see Text-Fig. 1. For legend, see Text-Fig. 3. Location of sections: a-Text-Fig. 2; b,c-Text-Fig. 3; d-Text-Fig. 4.
acid tuffs immediately above the Kalwang Conglomerate atit
slates grade into middle and late Devonian pelagic lime-
TARKIAN,
i,
stones and mid-Carboniferous shales.
The Silurian and early Devonian mafic volcanics that domi-
the
1984;
locality
Kalwang/Teichgraben
(SCHÄFFER
&
LoESCHKEetal., 1990).
At high levels of these basal phyllites conodonts of Caradocian age occur (FLAJS & SCHÖNLAUB, 1976). Recently,/,
REITZ & H O L L (1989) described palynomorpha of early Ordovician age within slates of a comparable section of the western Graywacke zone.
nate the westerly adjacent areas (SCHÖNLAUB, 1982; HEINISCH et al., 1988; SCHLAEGEL-BLAUT, 1990) apparently do
not occur within the area of investigation. The age of deformation is younger than Namurian A (latest sediments in a
Carboniferous crinoidal breccia) and older than the supposed early Permian age of the transgressive Prebichl formation. The angular unconformity prove some (two or three)
Variscan nappes as well as semiductile folding and faulting
The Blasseneck porphyroid is of ignimbritic origin (HEI-iy
NISCH, 1 9 8 1 ; LOESCHKEet al., 1990) and is locally overlain by
h
the Petersbauerngraben Fm., a metaconglomerate which
$_ (SCHÖNLAUB, 1982; NEUBAUER, 1989).
may extend to the west into the Polster Quartzite (FLAJS &
s
S C H Ö N L A U B , 1976; STATTEGGER, 1982) and further continues
A Rb-Sr thin slab isochrone of the Carboniferous slates
k
into black slates and cherts (HERMANN, 1992). Laterally, thick
!)
slates and phyllites occur (Rad Phyllite: CORNELIUS, 1952)
y
containing another acidic tuff layer of late Silurian or early
e
Devonian age, greywackes and lydites (NIEVOLL, 1987). The
yielded an age of 246 Ma (JUNG, 1980). Detrital white micas
yield a maximum model age of approximately 320 Ma that
falls within reasonable proximity to the supposed age of the
Variscan metamorphism in the source region.
70
F. NEUBAUER, R. HANDLER, S.HERMANN &G. PAULUS
Tectonic Units
Stratigraphic Units
limestones and dolomites
(Anisian - Turanian)
Northern Calcareous Alps
sandstones and Vermcano-type
conglomerates (Permo-Scythian)
Prebichl and Werfen Fm.
limestones and dolomites
(Devonian - Upper Carboniferous)
shales and sandstones
(Upper Ordovician - Lower Devonian)
Noric Nappe
acidic metatuff
(Caradocian)
Blasseneck Porphyroid
phyllites and sandstones
(Ordovician)
( i f eg
conglomerate with dominance
of gneiss boulders
Kaintaleck Nappe
V
r^
<
Silbersberg Nappe
^ ~ j
o;.:
amphibolites and micaschists
(pre-Variscan metamorphism)
phyllites, sandstones, and Verrucano-type
conglomerates (Permo-Scythian)
# # • • • • • • • • '
»••••••••*"-
oy.o
Veitsch Nappe
c
• i-H
riebeckite
Rad Phyllite
Gerichtsgraben Fm.
Kalwang Conglomerate
Kaintaleck Metamorphic
Complex
Silbersberg Conglomerate
Gloggnitz Riebeckite Gneiss
gneiss
quartzphyliites and calcareous phyllites
(Early Paleozoic)
Quartzphyllite
phyllites and sandstones
(Permo-Scythian)
Graschnitz Fm.
shales, sandstones, and conglomerates
(Westphalian A - C)
Sunk Fm.
shales and limestones
(Early Visean - Namurian)
Triebenstein Fm.
shales, sandstones, and conglomerates
(Early Visean)
Steilbachgraben Fm.
limestones, sandstones, and Verrucano-type
MidTriassic)
conglomerates (Permian - Mid
Triassic)
P n n r i Q p n THTV»
JVaUIldUl .Fill.
amphibolites and micaschists
(Variscan metamorphism)
Rennfeld and Mugel
Complex
- s
Text-Fig. 6.
Tectonostratigraphy of the eastern Graywacke Zone.
3. Alpidic vs. Pre-Alpidic Metamorphism
ages ranging from 413 to 355 Ma (DALLMEYER et al., 1992;
The eastern Graywacke Zone is believed to have been
penetratively overprinted by Alpidic greenschist facies metamorphism. The basic observations supporting that, are
the complete penetrative ductile deformation of the Veitsch
nappe, which apparently does not exhibit pre-Alpidic ductile
fabrics (RATSCHBACHER, 1986), Cretaceous K-Ar muscovite
ages from the western portions of the eastern Graywacke
Zone (RATSCHBACHER, 1984), and mineral parageneses
which are formed within greenschist facies conditions. Temperature conditions have been estimated as high as 500°C
immediately to the west of the area of investigation (RATSCH-
40
BACHER & KLIMA, 1985).
Mineral parageneses in post-Variscan sediments from the
Veitsch nappe include:
1) actinolitic amphibole + chlorite + green biotite + albite +
quartz + sphene in mafic rocks; and
2) quartz + white mica (muscovite) +/- albite +/- chlorite in
metapelites and metasandstones.
On the other hand, recent Rb-Sr and mineral ages from
the basement rocks, especially those of the Kaintaleck
Complex, clearly show the presence of pre-Alpine mineral
HANDLER et al., 1992, submitted; HERMANN, 1992). The
Ar/39Ar muscovite spectra indicate no loss of radiogenic
argon due to Alpine overprint. We conclude therefore, that
Alpidic metamorphism did not significantly exceed 400°C in
the area of investigation.
4. Alpidic Ductile Deformation
Late Paleozoic and early Triassic cover sediments, especially the Veitsch Group and the Silbersberg Conglomerate,
exhibit a penetrative foliation including a mineral or stretching lineation, respectively. The foliation generally dips towards NNW, the stretching lineation is generally subhorizontal and trends W to NW in the area Brück a.d. Mur towards Trofaiach and SW in the sectors between Trofaiach
and Vöstenhof. In accordance with previous investigations
in the westerly adjacent areas general displacement during
nappe stacking is top to the W or NW, respectively, due to
shear sense indicators that have been formed during penetrative ductile deformation in cover sediments (NIEVOLL,
1983;
RATSCHBACHER, 1986;
RATSCHBACHER & OERTEL,
71
Revised Lithosi rattgraphy and Structure of the Eastern Graywacke Zone (Eastern Alps)
1987; NEUBAUER et al., 1987; RATSCHBACHER & NEUBAUER,
1989). The presence of these fabrics in the Permo-Triassic
cover sequences clearly proves the Alpine age of the penetrative deformation.
5. Discussion
From a lithological point of view, the stratigraphy presented here has been basically well known for a long time
(for summary, see TOLLMANN, 1977). Especially, the stratigraphic succession between the Veitsch nappe and the
Kaintaleck Complex in the easternmost portions of the
Graywacke Zone near Gloggnitz has been completely
patched up to the Noric nappe (TOLLMANN, 1977; DAURER &
SCHÖNLAUB, 1978; SCHÖNLAUB, 1979). Metamorphic rocks
of the Kaintaleck Complex were believed to be included with
those of the Noric nappe, although the successions below
and above the Kaintaleck Complex are completely different
from each other. Consequently, the Gloggnitz Riebeckite
Gneiss have been compared with the Blasseneck Porphyroid and an Ordovician age was suggested
(e.g.,
CORNELIUS,
1941; KOLLER & ZEMANN,
1991).
The age data (Tab. 1)
from the Kaintaleck
Complex (HANDLER et
al., submitted; NEUBAUER & FRISCH, 1993) indi-
cate that this Complex
was not subjected to
any major Variscan metamorphic
overprint.
This fact contrasts with
the Variscan metamorphic overprint of the adjacent Rennfeld-Mugel
Complex to the south
(part ofthe Muriden units;
NEUBAUER,
FRISCH
1989;
lationships between portions of the Kaintaleck Complex and
the Veitsch nappe cannot be ruled out.
The new stratigraphic and tectonic divisions bear some
importance to the Alpine paleogeography which we discuss
here in a qualitative way. It is obvious from many sections,
that the cover sequences of the Middle Austroalpine nappe,
the Veitsch nappe and the Silbersberg nappe only include
basal Permian and Triassic portions (Text-Fig. 7). Restoring
in a qualitative way (for basic methods, see BOYER & ELLIOT,
1982), assuming a general NW transport during Alpine
thrusting (e.g., RATSCHBACHER, 1986), the pre-thrusting arrangement of the Permian and Triassic sequences from present NW to SE is as follows: the Middle Austroalpine unit,
Veitsch nappe, Silbersberg nappe, Kaintaleck nappe and
Noric nappe as well as other nappes of the Northern Calcareous Alps. In this arrangement it is obvious that within northern portions of the Northern Calcareous Alps the basal stratigraphic portions are missing suggesting preservation within the other three nappes.
Our new data suggest a further aspect for large-scale regional correlation, namely the presence of two nappes con-
1988b;
&
NEUBAUER,
NEUBAUER
&
FRISCH, 1993). This difference underlines the
importance of the Noric
Thrust along which the
Kaintaleck Complex has
been emplaced. On the
other hand, primary
Tectonostratigraphic
unit
Protolith
ages
NORIC NAPPE:
Basal Northern
Calcareous Alps
Permian to
Cenomanian
Noric Group
KAINTALECK NAPPE:
Kalwang(?)
Conglomerate
Kaintaleck
Complex
SILBERSBERG NAPPE:
Silbersberg
Conglomerate
NEUBAUER et al. (1987),
NEUBAUER (1988a), DALLMEYER et al. (1992), HANDL-
ER (1994), HANDLER et al.
(1992, submitted) and NEUBAUER & FRISCH (1993).
greenschist
facies
320 - 310
140 - 120
post-Middle
Devonian
pre-Devonian
VEITSCH NAPPE:
Veitsch Group
MIDDLE AUSTROALPINE
NAPPE:
Liesing-Thörl
Groups
Rennfeld-Mugel
Complex
Age of
Alpine
metamorphic
overprint
(Ma)
140 - 120
polyphase
amphibolite f.
520 - 380
140 - 90(?)
?
Permian
140 - 110(?)
Gloggnitz
Riebeckite Gneiss
"Quartzphyllite"
Basement
Table 1.
Summary of stratigraphic
and geochronological data
of the Eastern Graywacke
Zone.
Geochronological data are
based on compilations and
data in FRANK et al. (1987),
Late Ordovician
to Visean(?)
Extent and
age (Ma) of
pre-Alpine
metamorphic
overprint
Ordovician
to Devonian
(?)
Early Carboniferous to
Early Permian
Permian Middle Triassic
L. Proterozoic
to E.Carboniferous
greenschist
—
100 - 80
100 - 80
100 - 80
polyphase
amphibolite f.
360 - 330
72
F. NEUBAUER, R. HANDLER, S. HERMANN & G. PAULUS
NORTHERN CALCAREOUS ALPS
WNW
ESE
\
LOWER
MIDDLE
AUSTROALPINE AA.
/A
•
VEITSCH SILBERS- KAINTAL- NORIC
NAPPE BERG
ECK
NAPPE
NAPPE
NAPPE
Middle Triassic to Cretaceous carbonate sequences
Clastics-dominated Carboniferous and PermoScythian sequences
Phyllitic pre-Late Carboniferous basement
Pre-Late Carboniferous basement within
amphibolite facies conditions
Text-Fig. 7.
Suggested restored paleogeography of eastern sectors of the Austroalpine units.
taining early Paleozoic phyllitic basement rocks with possibly early Paleozoic quartzphyllites in the Silbersberg Nappe
and early Paleozoic, mostly pelagic sediments in the Noric
Nappe. This relationship closely resembles the internal
structure of the Upper Austroalpine units in the Central Alps,
i.e. those of the Graz and Gurktal Nappe Complexes. In the
Gurktal Nappe Complex, the basement lithologies (mainly
quartzphyllites, greenschist and marbles) of the Murau Nappe could be largely compared with the Silbersberg Nappe
and those of the Stolzalpe Nappe with those of the Noric
Group. In the Graz Nappe Complex, lithologies of the
Schöckl-Anger Groups are similar t o the quartzphyllites of
the Silbersberg Nappe, the Noric Group has main equivalents in the pelagic Laufnitz Group within the Graz Nappe
Complex. These relationships argue for a major uniform Upper Austroalpine nappe system that covers the entire Middle
Austroalpine unit of the Central Alps.
6. Conclusions
From the data presented above and discussions w e
conclude:
O
The eastern GraywackeZone is composed of four Alpine
thrust sheets.
Q Major portions of the Kaintaleck Complex do not represent the basement of the early Paleozoic Noric Group.
0 The metamorphic Kaintaleck complex strongly contrasts in time the Variscan metamorphism within the
Middle Austroalpine basement.
O The Silbersberg nappe between Veitsch and Kaintaleck
nappes includes both a quartzphyllitic basement and a
Permian (?) cover sequence.
0 The Alpine metamorphic overprint in the eastern Graywacke Zone did not significantly exceed 3 5 0 - 4 0 0 ° C .
0 The pre-Alpine tectonothermal overprint is, therefore,
well preserved in the eastern Graywacke Zone.
Acknowledgements
We acknowledge valuable suggestions by formal reviews from
Helmut HEINISCH (Gießen) and Hans-Peter SCHÖNLAUB (Vienna). The
work has been supported by the Austrian Science Funds (grants
P7405-GEO and P8652-GEO).
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Manuscript received: 28.12.1992
Revised version received: 21.07.1993
Manuscript accepted: 06.10.1993
•
•
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